Why does this code decompress a UIImage so much better than the naive approach?

Question

In my app I need to load large JPEG images and display them in a scroll view. In order to keep the UI responsive, I decided to load the images in the background, then display th

Answer 1

I assume that you're running this on a Retina device. In UIGraphicsBeginImageContextWithOptions, you asked for the default scale, which is the scale of the main screen, which is 2. This means that it's generating a bitmap 4x as large. In the second function, you're drawing at 1x scale.

Try passing a scale of 1 to UIGraphicsBeginImageContextWithOptions and see if your performance is similar.